1. Field of the Invention
The present invention relates to a substrate processing apparatus and a substrate processing method for processing substrates with process liquids. Examples of substrates to be processed include semiconductor wafers, glass substrates for liquid crystal displays, glass substrates for plasma displays, substrates for FEDs (field emission displays), substrates for optical discs, substrates for magnet-optical discs, glass substrates for photomasks, substrates for ceramics, substrates for solar cells, etc.
2. Description of Related Art
In the manufacturing steps of semiconductor or liquid crystal display apparatus, hydrofluoric acid is supplied onto substrates such as semiconductor wafers, glass substrates for liquid crystal displays, to conduct etching step for eliminating unwanted film from substrates or cleaning step for eliminating particles from substrates. For example, JP-A-2001-15481 discloses a substrate etching apparatus for etching substrates. In this etching apparatus, hydrofluoric acid vapor, filled in a chamber accommodating substrates, is supplied onto a substrate. Supplying of hydrofluoric acid vapor toward substrates is conducted while exhaust of gas in the chamber is being conducted.
Vapor etching with HF vapor (vapor that contains hydrofluoric acid) has inherent problems that are distinguished from problems encountered in so-called wet etchings. In vapor etching, HF vapor condensates on a substrate, changing its state from gas to liquid. Droplets of liquid formed by the condensation aggregate to form condensed state liquid (HF condensed state liquid) containing hydrofluoric acid and water on the substrate. As the condensation process takes place on the entirety of the substrate, the vapor continues to condense in drops; which coalesce and grow to be a film-like HF condensed state formed on the whole substrate area. Water on or around the substrate dissolves into the HF condensed phase liquid.
Processing substrates with HF vapor would typically take about several 10 seconds to several 10 minutes, depending on HF density or types of substrate. Substrate etching is sustained as long as HF vapor supply to the substrate is maintained. Because HF component in HF vapor is consumed by etching processing, new HF vapor is required to be replenished onto the substrate. Therefore, it is required that HF vapor be supplied onto the substrate in an uniform flow rate across the substrate, in order to uniformly etch the whole substrate area.
In a case of an etching apparatus described in JP-A-2001-15481, HF vapor is exhausted at a given exhaust flow rate out of its chamber during its operation. This tends to incur bias in the HF vapor flow across its substrate, and accordingly bias in HF density distribution within its etching chamber. Thus a non-uniform condensed phase could be formed on the substrate, which can cause resultant unevenness of the substrate processing. The unevenness should be particularly conspicuous for etching on peripheral portions of substrates wherein relative pace of etching thereof slows down, to degrade process uniformity. Such degradation of process uniformity can happen not only in cases of substrate processing with hydrofluoric acid vapor, but also with vapor containing components other than hydrofluoric acid.